Green-Synthesized Strontium-Doped Carbon Dots from Walnut Shells for Sensitive AFB1 Detection: Structural and Energetic Insights

Aflatoxin B1 (AFB1) is a highly toxic mycotoxin that poses a serious threat to food safety and human health. To achieve rapid, sensitive and specific detection of AFB1, a label-free D-shaped optical fiber sensor based on lossy mode resonance (LMR) was developed in this study. The sensor was fabricated by depositing a SnO2 thin film on the polished surface of a D-shaped optical fiber as the LMR sensitive layer and immobilizing anti-AFB1 antibodies on the SnO2 surface to construct a specific biorecognition interface. The specific binding between AFB1 in the sample and the immobilized anti-AFB1 antibodies causes a change in the effective refractive index (RI) on the fiber surface, thereby causing variation in transmission spectrum. Experimental results show that the fabricated sensor exhibits a good response to AFB1 in the concentration range of 0.1-100 ng/mL with excellent specificity. The sensor's limit of detection (LOD) was approximately 0.071 ng/mL. In addition, the proposed D-shaped optical fiber LMR sensor was successfully applied to the detection of AFB1 in real food samples such as peanuts, corn, wheat, and millet, which provided a promising approach for the rapid and sensitive detection of AFB1 in food and agricultural samples, with broad application prospects in food safety supervision.

We evaluated whether aflatoxin B1 (AFB1 ) exposure was associated with later risk of developing gallbladder cancer (GBC). We measured AFB1 -lysine albumin adducts in baseline samples from the Shanghai Cohort Study of 18 244 men aged 45 to 64 years (recruited 1986-1989). We included 84 GBC cases with sufficient serum and 168 controls matched on age at sample collection, date of blood draw and residence. We calculated adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs) for detectable vs non-detectable AFB1 -lysine albumin adducts and gallbladder cancer. AFB1 -lysine albumin adducts were detected in 50.0% of GBC cases, and risk of GBC was twice as high in those with detectable vs undetectable levels (OR = 2.0, 95% CI = 1.0-3.9). ORs ranged from 1.8 (95% CI = 0.75-4.3) for 0.5 to <1.75 pg/mg vs undetectable adduct levels to 2.2 (95% CI = 0.91-5.6) for >3.36 pg/mg vs undetectable, suggesting a dose-response (Ptrend = .05). When restricted to cases diagnosed before the median time to diagnosis after blood draw (18.4 years), results were similar (OR = 2.2, 95% CI = 0.80-5.8) to those for the entire follow-up duration. The OR was 9.4 (95% CI = 1.7-51.1) for individuals with detectable AFB1 -lysine albumin adducts and self-reported gallstones compared to individuals with neither. Participants with detectable AFB1 -lysine albumin adducts at baseline had increased risk of developing GBC, replicating the previously observed association between AFB1 exposure and providing the first evidence of temporality.

Carbon quantum dots from carbonized walnut shells: Structural evolution, fluorescence characteristics, and intracellular bioimaging

Carbon quantum dots (CQDs), with their remarkable optical properties such as strong fluorescence and biocompatibility, are emerging as versatile tools in biosensing and food safety monitoring. This study investigates binding-induced Förster resonance energy transfer (FRET) between CQDs as donors and aflatoxin B1 (AFB1), a highly toxic mycotoxin, as the acceptor. Spherical CQDs, averaging 4.56nm in diameter and emitting fluorescence at 455nm, were synthesized for this purpose. Fluorescence spectroscopy, incorporating Stern-Volmer analysis and time-resolved lifetime measurements, revealed the critical role of FRET in this interaction. The estimated Förster radius (R0) of 4.81nm and donor-acceptor separation distance (r) of 5.12nm corresponded to a FRET efficiency of 46%. The observed decrease in donor fluorescence lifetime further supports the FRET mechanism. Selectivity experiments confirmed the system's specificity for AFB1 detection, with a limit of detection (LOD) of 0.439 nM. These findings underscore the potential of FRET-based CQD systems for sensitive and selective AFB1 detection, highlighting their versatility in fluorescence-based sensing applications and their promise for rapid food safety monitoring.

Aflatoxin B1 (AFB1) monitoring has attracted extensive attention because food safety is a worldwide public health problem. Herein, we design a novel simultaneously visual and photoelectrochemical (PEC) immunosensing system for rapid sensitive detection of AFB1 in foodstuff. The immunoreaction was carried out on anti-AFB1 antibody-modified magnetic beads by using glucose oxidase (GOx)-labeled AFB1-bovine serum albumin (AFB1-BSA) conjugates as the tags with a competitive-type immunoassay format, while the visual and PEC evaluation was performed via carbon quantum dots (CQDs)-functionalized MnO2 nanosheets. Accompanying the formation of immunocomplexes, the carried GOx initially oxidized the substrate (glucose) for the generation of H2O2, which reduced/etched MnO2 nanosheets into Mn2+ ions, thereby resulting in the dissociation of CQDs from the electrode. Within the applied potentials, the photocurrent of MnO2-CQDs-modified electrode decreased with the increasing H2O2 level in the detection cell. Meanwhile, a visual detection could be performed according to the change in the color of MnO2-CQDs-coated electrode. To elaborate, this system was aggregated into a high-throughput microfluidic device to construct a semiautomatic detection cell. Under optimal conditions, the photocurrent increased with the increasing target AFB1 within a dynamic working range from 0.01 to 20 ng mL-1 with a limit of detection (LOD) of 2.1 pg mL-1 (ppt). The developed immunoassay exhibited good reproducibility and acceptable accuracy. In addition, the method accuracy relative to AFB1 ELISA kit was evaluated for analyzing naturally contaminated or spiked peanut samples, giving the well-matched results between two methods. Although our strategy was focused on the detection of target AFB1, it is easily extended to screen other small molecules or mycotoxins, thereby representing a versatile immunosensing scheme.

In recent years, bio-based polymers and fillers are attracting the attention of researchers due to strong concerns on environmental friendly production of rubbers. In this study, the waste walnut shell was used as an alternative filler for ethylene–propylene–diene monomer rubber (EPDM). The surface of the waste walnut shell was modified with bis[3-(triethoxysilyl)propyl] tetrasulfide to achieve a better interfacial interaction with EPDM matrix. Effect of different parameters on mechanical, thermal, and rheological properties of EPDM/waste walnut shell filler composite was investigated. It was seen that the increase of walnut shell content led the increase in tensile strength. Moving die rheometer tests have shown that the addition of walnut shell improved the torque value. In addition, the thermal tests were shown that using the waste walnut shell as filler results with no considerable difference in the thermal properties. Swelling test and cross-link density analyses showed that walnut shell addition has no negative effect on cross-link density. It was concluded that the waste walnut shell could be an effective filler with its advantages of bio-based and biodegradable.

Aflatoxin B1 (AFB1) is one of the mycotoxins with the most dangerous poisons and poses a threat to living things. Several detection methods for Aflatoxin B1 (AFB1) with high sensitivity (LC-MS technique, HPLC, ELISA, etc.) still require lengthy preparation time and are not real-time and portable. Aflatoxin B1 (AFB1) detection is one of the major challenges in the field of food safety because Aflatoxin B1 (AFB1) attacks the food and agricultural products sector. One of the potential sensors that can be used as a base for Aflatoxin B1 (AFB1) detection is the Quartz Crystal Microbalance (QCM) sensor. This study examines the performance of the Quartz Crystal Microbalance (QCM) sensor as one of the Aflatoxin B1 detection techniques through the physical deposition method. The Quartz Crystal Microbalance (QCM) sensor modified uses polyvinyl acetate (PVAc) material as a container to embed a molecular model that will be detected through a molecular imprinting polymer (MIP) process coated on QCM using the electrospinning method. The response results show that the value of the sensor response using the MIP process is more significant than without the MIP process. The sensor characteristics demonstrated by the PVAc/AFB 50 sample have a limit of detection (LOD) value is 0.63 ppb, and a limit of quantitation (LOQ) is 1.91 ppb with a coefficient correlation is 0.97 for testing with a concentration range of 5.0 – 40.0 ppb. Therefore, the MIP process in QCM provides a favorable response for the detection of AFB1 in the future.

In this study, we present a facile and efficient method for fabricating silk fibroin hydrogel films encapsulating the acetylcholinesterase enzyme (AChE) and pH test strips (biosensor strips) for detecting organophosphorus pesticides (OPs) and aflatoxin B1 (AFB1). These biosensor strips possess several unique properties: flexibility, time efficiency, and high stability. Upon exposure to OPs or AFB1, AChE activity is inhibited, leading to a discernible color change on the pH test strip, enabling rapid and sensitive visual detection of these contaminants. The strips were effectively utilized as a practical and sensitive platform for the visual detection of OPs and AFB1. The limits of detection for paraoxon, aldicarb, and AFB1 were determined to be 6.57, 8.92, and 0.274 ng mL-1, respectively. Furthermore, the applicability of these biosensors for detecting OPs or AFB1 in real samples of Chinese cabbage and peanuts was successfully demonstrated. Additionally, the performance of these novel strip composites was validated through comparison with commercial pesticide rapid test papers. Notably, the encapsulated AChE enzymes retained significant sensitivity for over 18 months, even when stored at 37 °C, and the biosensor strips exhibited remarkable resistance to sensitivity loss caused by inhibitors. This work presents a highly sensitive and stable enzyme-based visual detection paper for agricultural and food safety applications. In addition to its outstanding resistance to interference, the developed biosensor ensures reliable reproducibility and maintains stability over long-term use. This new approach to OP analysis in ecological samples has also been effectively used in the determination of OPs in lake water.

Bimetallic nanozyme–bioenzyme hybrid material-mediated ultrasensitive and automatic immunoassay for the detection of aflatoxin B1 in food

The synthesis of cobalt, nitrogen and sulfur co doped carbon quantum dots (Co-NS-CQDs) has become a subject of significant research interest. These CQDs were produced using a single-step microwave method, which is considered environmentally friendly, and the entire process was completed in just 90 seconds. In this synthesis, citric acid was utilized as the carbon source, methionine served as the source for both nitrogen and sulfur, and cobaltous acetate was used to introduce cobalt ions into the CQDs structure. The synthesized carbon quantum dots (CQDs) exhibit a narrow size distribution and a high quantum yield of 51.5%, which is notably superior to non-metal-doped CQDs with a yield of 38%. Characterization of these CQDs was performed using different techniques such as transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transformation infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The developed CQDs have blue luminescence at emission wavelength 438 nm after excitation at 350 nm. Different factors affecting the CQDs synthesis including dialysis duration, reaction time and reaction temperature. These CQDs were utilized as a probe for the detection of monosodium glutamate (MSG) in various food products. The intensity of the fluorescence of the CQDs showed a direct and linear increase with the concentration of MSG within the range of 25–250 µg/mL. The detection and quantitation limits for MSG were 2.78 µg/mL and 8.44 µg/mL, respectively. Additionally, the developed method is environmentally friendly, as confirmed by assessments using the analytical Eco scale, Green Analytical Procedure Index (GAPI), and Analytical Greenness calculator (Agree). The proposed method presents several advantages over other reported methods in terms of convenience, rapid response, and attainment of accurate and precise results.

A label-free fluorescent aptasensor for the detection of Aflatoxin B1 in food samples using AIEgens and graphene oxide

A metal-organic framework/aptamer system as a fluorescent biosensor for determination of aflatoxin B1 in food samples

Sensitive and selective detection of trace aflatoxin B1 (AFB1) in foods is of great importance to guarantee food safety and quality but still challenging because of its trace amount and the interference from the complex food matrix. Here, we report the integration of aptamer (Apt) and an ordered 2D covalent organic framework (COF) to solid-state anodic aluminum oxide (AAO) nanochannels (Apt/COF/AAO) for selective and sensitive detection of trace AFB1. The high specificity of Apt for AFB1 led to a selective change in the surface charge of Apt/COF/AAO and in turn the current change of the nanochannel, permitting the selective and sensitive determination of trace AFB1 in complex food samples. The developed nanofluidic sensor gave a wide linear range (1-500 pg mL-1), low detection limit (0.11 pg mL-1), and good precision (relative standard deviation of 1.5% for 11 replicate determinations of 100 pg mL-1). In addition, the developed sensor was successfully used for the detection of AFB1 in food samples with the recovery of 86.9%-102.5%. The coupling of Apt-conjugated 2D COF with an AAO nanochannel provides a promising way for sensitive and selective determination of food contaminants in complex samples.

Evolution of large stokes shift and non-radiative energy transfer phenomenon in sustainable blue-fluorescent CQDs upon subnanomolar detection of Acebrophylline.

This project focuses on the development of a DNA-aptamer based biosensor, which is referred to as an aptasensor, that would aid in the detection of mycotoxins in foodstuffs. We developed aptamer based biosensor for detection of Aflatoxin B1 (AFB1), a mycotoxin produced by Aspergillus flavus and Aspergillus parasiticus, species of fungi. The characterization of the sensor and detection of aflatoxin B1 was performed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). We tested an electrochemical aptasensor for AFB1 detection through the immobilization of DNA aptamers on the Poly (amido-amine) dendrimers of fourth generation (PAMAM G4) on gold electrode covered by cystamine. The DNA aptamers specific to AFB1 were attached on the PAMAM layer covalently by means of glutaraldehyde. The range of AFB1 concentrations was selected as target interval for further utilization of the biosensor in food samples. The aptasensor has been tested in certificated samples of peanuts as well as in spiked samples of peanuts demonstrating optimal response. The biosensor was also tested in other mycotoxins such as ochratoxin A (OTA) and aflatoxin B2 (AFB2), to investigate non-specific interaction.